1. Field of the Invention
This application relates to orbital tools and in particular, small handheld palm sanders.
2. Background Art
Orbital palm sanders are widely used for a variety of sanding operations from woodworking to auto body repair. Orbital palm sanders come in two general types; random orbit sanders and pad sanders. Random orbit sanders typically have a round sanding platen which supports a sandpaper disc mounted on a central pivot bearing which is rotated about an orbital path. The sanding platen moves in an orbital pad but, is otherwise free to rotate about a bearing. Pad sanders are typically very similar in construction to a palm-type random orbit sander, however, the sanding platen is constrained so that it can orbit, but cannot freely rotate relative to the housing. An example of such a tool is a quarter sheet sander having a generally square sanding platen. A third variant, although not common, is an eccentric sander where the sanding platen orbits at high speed about the motor axis while being slowly rotated by an eccentric gear pair.
Orbital palm sanders are generally small and compact, and have a motor axis which extends perpendicular to the sanding platen. The output end of the motor is connected to the sanding platen by an eccentrically located drive bearing. In the case of the random orbit sander, the bearing is the sole connection between the platen and the eccentric drive. In the case of the pad sander, a sanding platen will be restrained from rotating by elastomeric elements. In the case of an eccentric sander, the sanding pad rotation relative to the housing will be controlled by an eccentric gear pair.
Orbital sanders are frequently provided with a dust collection feature. In order to collect dust, the sanding platen will have a series of apertures formed therethrough corresponding to matching apertures in the sandpaper. An internal fan associated with the eccentric drive cooperates with a chamber in the motor housing to extract air and dust through the sanding platen and discharge the air dust through an outlet port connected to a dust canister or a remote collector vacuum. The eccentric drive and fan assembly is frequently made of die cast zinc and commonly includes a cast counterweight sized to balance the eccentric drive fan and sanding platen sub assembly relative to the motor axis. The eccentric drive fan counterweight assemblies are typically individually balance tested and machined in order to compensate for part to part manufacturing variability, particularly in higher price palm sanders where a smooth balance is desired.
The orbital sander embodiment of the present invention contains a number of novel features. The preferred sander embodiment is driven by a high speed permanent magnet DC motor which has a relatively flat RPM versus torque curve. As a result, the motor decreases in speed relatively little from the no load speed in contrast to universal motors employed in the prior art. The preferred embodiment drops in speed less than 25% when the load is increased from the no load speed to the maximum continuous operating rated load.
Additionally, the preferred embodiment of the invention utilizes a novel eccentric drive and fan member where the fan is provided by an annular disc extending normal to the motor axis having a series of integrally formed blades circumaxially spaced about the disc in a non-uniform manner. The relative concentration of fan blades in one region of the discs and the sparse spacing of fan blades in a diametrically opposite region results in an imbalance which is used to counter-balance the eccentrically offset sanding platen which is pivotally attached thereto without using a conventional balance weight. This prevents casting irregularities resulting in poor balance control.
The preferred embodiment further has a unique on/off switch and switch actuator. The on/off switch is located internal to the housing and a switch actuator bar extends transversely through the housing, lying in a plane perpendicular to the motor axis. The switch actuator bar has two opposed ends. At least one end extends from the housing at all times, enabling the operator to switch between the on and off position by pushing on the opposed ends of the actuator bar located transversely on opposite sides of the housing per portion.
The orbital sander further has a novel dust collection outlet port which facilitates the use of a dust collection cannister or two alternative sized dust collection vacuums.
The above novel features, as well as other advantages and characteristics of the present invention will be readily appreciated by one of ordinary skill of the art from the reviewing the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.